Multiple Sclerosis (MS) and its animal model (experimental autoimmune encephalomyelitis; EAE) are autoimmune disorders of the CNS, and are considered to be mediated by myelin reactive T helper cells (TH1, TH2, Treg and TH17). The present proposal is to investigate S-nitrosoglutathione (GSNO)-mediated immuno- modulation and neuroprotection/neurorepair mechanisms in EAE disease models based on our novel finding that: 1) GSNO attenuated disease in three different EAE disease models; SJL mice immunized with PLP139-151, C57BL/6 mice immunized with MOG35-55, and Lewis rats immunized with MBP; 2) GSNO inhibited TH17 polarization/effector functions and induced Treg polarization/effector functions without obvious effects on TH1 and TH2; 3) GSNO-mediated post-translational modification of STAT3 (S-nitrosylation at Cys259) inhibited STAT3 activation which plays a critical role in TH17/Treg polarization/effector functions and disease progression of EAE/MS; 4) GSNO inhibited NFkappaB activity and iNOS expression which play a critical role in oxidative/nitrosative damage of the CNS under inflammatory conditions;.5) GSNO induced astroglial expression of neurotrophic factors that play a critical role in the neurorepair process. Based on these novel findings, we hypothesize that GSNO-mediated mechanisms attenuate the EAE/MS disease by S-nitrosylation and inhibition of STAT3 and also promote neuroprotection and neurorepair processes in EAE by attenuation of NFkappaB/iNOS-mediated nitrosative/oxidative stress while still supporting cellular requirements for GSNO/NO with supplementation of GSNO. The proposed studies will test the hypothesis by investigating the role of GSNO in TH17/Treg polarization and neuroprotection/neurorepair processes and in EAE disease processes using genetic (iNOS knockout and GSNO reductase knock mice) as well as pharmacological approaches by using inhibitor of GSNO reductase (N6022) to increase endogenous GSNO and by supplementation of exogenous GSNO. Cellular homeostasis of GSNO is maintained by its redox based synthesis from GSH and NO and its enzymatic inactivation/degradation primarily by GSNO reductase (GSNOR). The proposed studies are: Specific Aim 1: To evaluate the efficacy of exogenous vs. endogenous GSNO on Treg/TH17 specific immunomodulation in an active EAE disease model. Specific Aim 2: To evaluate the efficacy of exogenous vs. endogenous GSNO on Treg/TH17 specific immunomodulation in the adoptive transfer passive EAE disease model. Specific Aim 3: To evaluate the efficacy of GSNO on neuroprotection and neurorepair in the EAE disease model. The novelty of the study is the promise of new therapeutic targets for TH17-mediated immune response and neuroprotection (protection of blood brain barrier and CNS) and promotion of neurorepair without affecting natural immuno-surveillance mechanisms mediated by other TH cells (e.g. TH1 and TH2). We expect that study of the S-nitrosylation-based regulatory mechanisms of TH17/Treg polarization/effector functions and neuroprotection/neurorepair in EAE disease will not only delineate the NO/GSNO mediated mechanisms in autoimmune disease, but also its clinical relevance as novel NO based therapeutics either alone or in combination with approved drug for MS. GSNO is a natural component of the human body and its exogenous administration in humans was not associated with any adverse effects. Therefore, potential use of GSNO by itself or in combination with present day medications as a translational drug for MS is promising and highly relevant to Veterans' health and the VA mission.